Electrochemical cell and method of preparing an electrode

Abstract

The present disclosure relates to an electrochemical cell comprising: an anode comprising a catalyst consisting essentially of ruthenium (Ru) disposed on a substrate, wherein the ruthenium is present as a film with a thickness of about 0.1 urn to about 1.0 pm; a cathode; and an exchange membrane separating the anode and the cathode. The present disclosure also relates to a method of preparing an electrode, an electrochemical cell comprising the electrode as disclosed herein and uses of an electrochemical cell as disclosed herein in water splitting, ammonia cracking, or as a fuel cell.

Description

[0001] Electrochemical Cell and Method of Preparing an Electrode

[0002] Cross-Reference to Related Applications

[0003] This application claims priority to Singapore application no. 10202403080V filed with the Intellectual Property Office of Singapore on 3 October 2024, the contents of which is hereby incorporated by reference in its entirety for all purposes.

[0004] Technical Field

[0005] The present disclosure generally relates to electrochemical cells, and more particularly relates to electrochemical cells comprising ruthenium anodes as well as uses thereof. The present disclosure also relates to methods of producing electrodes.

[0006] Background

[0007] Currently, around 4% of the global hydrogen production is generated by electrolysis. It is predicted that proton exchange membrane water electrolysis (PEMWE) technologies will play a large part in increasing the amount of green hydrogen produced from 4% of the global hydrogen production to about 30% by 2030. PEM water electrolyzers generally outperform conventional alkaline electrolyzers in voltage efficiency, gas purity, operational feasibility, response time, as well as compactness, and thus are considered one of the most promising solutions for green hydrogen production.

[0008] However, the main drawback of PEMWEs is the high cost of materials. Green hydrogen produced from PEMWEs currently costs about USD 3000 per kW, which is about 3 to 5 times the cost of green hydrogen produced from alkaline electrolyzers (about USD 700-1500 per kW). PEMWEs rely on expensive noble metals such as platinum (Pt), which is commonly used as a cathode in the hydrogen evolution reaction, as well as coating materials on gas-diffusion layers (which can be as thick as several hundred micrometers). Another expensive but commonly used noble metal is iridium, which is generally used as the anodic electrocatalysts for PEMWEs. While indium is durable and possesses high activity , it is scarce and therefore expensive, as evidenced by its 3-year average price of about USD 5000 / oz. This is around 5 times the cost of platinum (USD 950 / oz) and 13 times the cost of ruthenium (USD 420 / oz). Platinum and iridium account for approximately 33% of the total cost of PEMWEs.

[0009] In addition, the scarcity’ of indium raises concerns about long-term scalability and supply chain sustainability'. Given an average loading amount of about 3 mgir / cm2in conventional PEMWEs, it will be difficult to scale up to a projected goal of 10 GW / year of green hydrogen produced by’ PEMWEs.

[0010] Further, PEMWEs generally operate at operation potentials that will dissolve most metals, hence limiting the type of metals that can be used.

[0011] Thus, there is a need to provide an electrochemical cell that overcomes, or at least ameliorates one or more of the disadvantages described above. Summary

[0012] In an aspect of the present disclosure, there is provided an electrochemical cell comprising: an anode comprising a catalyst consisting essentially of ruthenium (Ru) disposed on a substrate, wherein the ruthenium is present as a film with a thickness of about 0.1 μm to about 1.0 μm; a cathode; and an exchange membrane separating the anode and the cathode .

[0013] Advantageously, the catalyst may exhibit increased OER activity and low overpotential. As an example, the catalyst may exhibit increased OER activity with a voltage of 1.48 V@0.4 A cnr2at a catalyst loading as low as 30 pg, and a low overpotential of 161 mV as compared to other ruthenium-based catalysts. Further advantageously, the catalyst may also exhibit increased stability (such as for example at least 7500 times) as compared to other ruthenium-based catalysts, which generally dissolve under OER operating conditions. The increased OER activity and stability may be achieved in acidic OER environments.

[0014] In another aspect of the present disclosure, there is provided a method of preparing an electrode comprising a catalyst consisting essentially of ruthenium (Ru), the method comprising the steps of: a) providing a solution of a Ru precursor at a concentration of about 1 pM to about 10 M in an acidic medium; and b) electrochemically depositing the Ru onto a substrate to achieve a Ru film with a thickness of about 0.1 μm to about 1 .0 μm, thereby forming the electrode.

[0015] Advantageously, the method of the present disclosure is widely applicable to various metal catalysts, conductive substrates, and facets. Further advantageously, the method of the present disclosure is also simple and easy to scale up. The method of the present disclosure is also a green process, which does not use any organic solvent, and allows dissolved Ru to be recycled for future use.

[0016] In a further aspect of the present disclosure, there is provided an electrochemical cell comprising the electrode produced by the method as disclosed herein.

[0017] In another aspect of the present disclosure, there is provided a use of an electrochemical cell as disclosed herein in water splitting, ammonia cracking, or as a fuel cell.

[0018] Definitions

[0019] Unless otherwise defined herein, scientific and technical terms used in this application shall have the meanings that are commonly understood by those of ordinary skill in the art. Generally, nomenclature used in connection with, and techniques of, chemistry described herein, arc those well- known and commonly used in the art.

[0020] Unless the context requires otherwise or specifically stated to the contrary, integers, steps, or elements of the invention recited herein as singular integers, steps or elements clearly encompass both singular and plural forms of the recited integers, steps or elements.

[0021] The word “substantially” does not exclude “completely” e g. a composition which is “substantially free” from Y may be completely free from Y. Where necessary, the word “substantially” may be omitted from the definition of the invention. As used herein in the specification and in the claims, the phrase "at least," in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every clement specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase "at least one" refers, whether related or unrelated to those elements specifically identified. Thus, as a non- limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B," or, equivalently "at least one of A and / or B") can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one. A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[0022] Unless specified otherwise, the terms "comprising" and "comprise", and grammatical variants thereof, are intended to represent "open" or "inclusive" language such that they include recited elements but also permit inclusion of additional, unrecited elements.

[0023] As used herein, the term "about", in the context of concentrations of components of the formulations, typically means + / - 5% of the stated value, more typically + / - 4% of the stated value, more typically + / - 3% of the stated value, more typically, + / - 2% of the stated value, even more typically + / - 1% of the stated value, and even more typically + / - 0.5% of the stated value.

[0024] Throughout this disclosure, certain embodiments maybe disclosed in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers withinthat range, for example, 1 , 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

[0025] Certain embodiments may also be described broadly and generically herein. Each of the narrower species and subgcncric groupings falling within the generic disclosure also form part of the disclosure. This includes the generic description of the embodiments with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein.

[0026] Brief Description of Drawings

[0027] The accompanying drawings illustrate disclosed embodiments and serve to explain the principles of the disclosed embodiments. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

[0028] Fig. 1A

[0029] Fig. 1 A is a digital photograph showing the morphology of ruthenium disposed on Ti mesh substrate according to an embodiment of the present invention at 0.5 mm scale.

[0030] Fig. IB Fig. IB is a Scanning Electron Microscopy (SEM) image showing the morphology of ruthenium disposed on carbon paper substrate according to an embodiment of the present invention at 2 μm scale.

[0031] Fig. 1C

[0032] Fig. 1C is an SEM image showing the morphology of ruthenium disposed on carbon paper substrate according to an embodiment of the present invention at 500 nm scale.

[0033] Fig. 1D

[0034] Fig. ID is an X-ray diffraction (XRD) spectrum of ruthenium on carbon paper substrate according to an embodiment of the present invention.

[0035] Fig. 1E

[0036] Fig. IE is an image of a ruthenium-based anode after stability test taken with a transmission electron microscope (TEM) at a scale of 1 nm.

[0037] Fig. 2

[0038] Fig. 2 is a graph showing the degradation rate of electrolyzers with anodes comprising Ru on carbon paper substrate, and Ru on Ti mesh substrate, compared to electrolyzers with anodes comprising commercial Ru, and commercial RuOz.

[0039] Fig. 3A

[0040] Fig. 3 A is a graph illustrating the OER performance of electrolyzers with anodes comprising Ru on carbon paper substrate, and Ru on Ti mesh substrate, compared with electrolyzers with anodes comprising commercial Ru, and commercial RuOz.

[0041] Fig. 3B

[0042] Fig. 3B is a graph comparing the activity and stability of an electrolyzer comprising Ru anode according to the present invention as compared with electrolyzers comprising Ru- and Ir- based anodes.

[0043] Detailed Disclosure of Embodiments

[0044] Exemplary', non-limiting embodiments of an electrochemical cell will now be disclosed.

[0045] The electrochemical cell comprises: an anode comprising a catalyst consisting essentially of ruthenium disposed on a substrate, wherein the ruthenium is present as a film with a thickness of about 0.1 μm to about 1.0 μm; a cathode; and an exchange membrane separating the anode and the cathode.

[0046] The anode may consist essentially of the ruthenium catalyst disposed on the substrate. The anode may consist of the ruthenium catalyst disposed on the substrate. The ruthenium catalyst may be predominantly metallic ruthenium . The ruthenium catalyst may be made up of 100% metallic ruthenium .

[0047] The thickness of the ruthenium film may be in a range of from about 0.1 μm to about 1.0 μm, from about 0.1 μm to about 0.9 μm, from about 0.1 μm to about 0.8 μm, from about 0.1 μm to about 0.7 μm, from about 0.1 μm to about 0.6 μm, from about 0.1 μm to about 0.5 μm, from about 0.1 μm to about 0.4 μm, from about 0.1 μm to about 0.3 μm, from about 0.1 μm to about 0.2 μm, or from about 0.2 μm to about 1.0 μm, from about 0.3 μm to about 1.0 μm, from about 0.4 μm to about 1.0 μm, from about 0.5 μm to about 1.0 μm, from about 0.6 μm to about 1.0 μm. from about 0.7 μm to about 1.0 μm, from about 0.8 μm to about 1.0 μm, from about 0.9 μm to about 1.0 μm, or about 0.1 μm, about 0.2 μm, about 0.3 μm, about 0.4 μm. about 0.5 μm, about 0.6 μm, about 0.7 μm, about 0.8 μm, about 0.9 μm, about 1 .0 μm, or any value or range therein. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that are within the stated rangc(s). The ruthenium film may be made up of nanocry stallitcs. Advantageously, the ruthenium film in the disclosed thickness may provide a larger active area than bulk Ru at the same loading, which may advantageously increase the OER activity of the ruthenium.

[0048] The ruthenium may be present or comprised in the anode at an amount of from about 0.01 mg / cm'2to about 0.50 mg / cm'2, from about 0.01 mg / cm'2to about 0.45 mg / cm'2, from about 0.01 mg / cm'2to about 0.40 mg / cm2. from about 0.01 mg / cm3to about 0.35 mg / cm2. from about 0.01 mg / cm2to about 0.30 mg / cm'2, from about 0.01 mg / cm'2to about 0.25 mg / cm'2, from about 0.01 mg / cm'2to about 0.20 mg / cm'2, from about 0.01 mg / cm'2to about 0.15 mg / cm'2, from about 0.01 mg / cm'2to about 0.10 mg / cm"2, from about 0.01 mg / cm'2to about 0.05 mg / cm'2, or from about 0.05 mg / cm'2to about 0.50 mg / cm'2, from about 0.10 mg / cm'2to about 0.50 mg / cm'2, from about 0.15 mg / cm'2to about 0.50 mg / cm'2, from about 0.20 mg / cm'2to about 0.50 mg / cm'2, from about 0.25 mg / cm'2to about 0.50 mg / cm'2, from about 0.30 mg / cm'2to about 0.50 mg / cm'2, from about 0.35 mg / cm'2to about 0.50 mg / cm'2, from about 0.40 mg / cm'2to about 0.50 mg / cm'2, from about 0.45 mg / cm'2to about 0.50 mg / cm'2, or about 0.01 mg / cm'2, about 0.05 mg / cm'2, about 0.10 mg / cm'2, about 0.15 mg / cm'2, about 0.20 mg / cm'2, about 0.25 mg / cm'2, about 0.30 mg / cm'2, about 0.35 mg / cm'2, about 0.40 mg / cm'2, about 0.45 mg / cm'2, about 0.50 mg / cm'2, or any value or range therein, based on the surface area of the substrate. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that are within the stated range(s).

[0049] The amount of ruthenium mentioned above may be referred to below as “loading” or “loading amount”.

[0050] In some embodiments, the amount of ruthenium loaded in the anode as disclosed herein corresponds to the thickness of the ruthenium on the substrate.

[0051] Advantageously, the electrochemical cell of the present disclosure may exhibit excellent OER performance at extremely low loading (such as that defined above) of the ruthenium catalyst and at a low overpotential. Tire low catalyst loading needed advantageously allows less ruthenium to be used in the assembly of the electrochemical cell, thus reducing manufacturing costs. Further advantageously, the electrochemical cell of the present disclosure may exhibit high stability.

[0052] The ruthenium may have a hexagonal closed packed (hep) structure. The ruthenium may have a (0001 ) facet or a (10-10) facet. Advantageously, a hep structure may provide a higher density of coordinatively unsaturated sites and step / edge terminations compared to amorphous or annealed phases. This structural feature may advantageously contribute to both higher intrinsic OER activity and enhanced stability, as the textured submicron sheets formed from hep nanocrystal I ites may be less prone to dissolution and may maintain their morphology even under acidic OER conditions.

[0053] The ruthenium may form a surface oxide film in situ. This may advantageously inhibit dissolution during OER, thereby drastically improving the OER stability of the ruthenium in acidic environments.

[0054] Advantageously, the catalyst may exhibit increased OER activity and low overpotential. As an example, the catalyst may exhibit increased OER activity with a voltage of 1.48 V@0.4 A cm'2at a catalyst loading as low as 30 pg, and a low overpotential of 161 mV as compared to other ruthenium- based catalysts. Further advantageously, the catalyst may also exhibit increased stability (such as for example at least 7500 times) as compared to other ruthenium -based catalysts, which generally dissolve under OER operating conditions. The increased OER activity and stability may be achieved in acidic OER environments. Further advantageously, only a small loading of about 0.01 mg / cm2to about 0.5 mg / cm2may be required for the catalyst loading, as compared to 2 to 4 mg of iridium required in conventional OER catalysts, which may lead to cost reductions of up to 1 / 1300 of the original cost.

[0055] The substrate may be a conductive substrate. The substrate may be selected from the group consisting of titanium (Ti), carbon (C), fluorinc-dopcd tin oxide (FTO), and glassy carbon .

[0056] The cathode may be a platinum catalyst disposed on a carbon substrate, or as appropriate depending on the use of the electrochemical cell. Tire anode as defined above may also be used as the cathode in the electrochemical cell. The inventors have surprisingly found that the catalyst is also suitable for use in hydrogen evolution reactions. Advantageously, this allows the replacement of a typical Pt / Ti cathode with a Ru / Ti electrode, which will reduce the costs of preparing the electrochemical cell.

[0057] Tire proton exchange membrane may be Nafion 115, Nafion 117, or Nafion 212.

[0058] Exemplary', non-limiting embodiments of a method of preparing an electrode comprising a catalyst consisting essentially of ruthenium will now be disclosed.

[0059] Tire method comprises the steps of: a) providing a solution of a ruthenium precursor at a concentration of about 1 pM to about 10 M in an acidic medium; and b) electrochemically depositing the ruthenium onto a substrate to achieve a ruthenium film with a thickness of about 0.1 μm to about 1.0 μm, thereby forming the electrode.

[0060] Advantageously, the method may be extended to produce ruthenium with different facets, such as (0001) or (10-10) facets. Further advantageously, the method may also be extended to the synthesis of other metals / alloys such as rhodium, palladium, silver, iridium, platinum, gold, manganese, iron, cobalt, nickel, copper, zinc, or combinations thereof.

[0061] Further advantageously, the method does not rely on organic solvent, thus making it a green process. Still further advantageously, the ruthenium dissolved in the precursor solution may be recycled and re-used for further electrodeposition, thus reducing production costs. Still further advantageously, the method may be suitable for large scale production. Further advantageously, the method only requires simple and inexpensive electrodeposition equiμment.

[0062] The precursor may be selected from the group consisting of RuCl? and ruthenium acetate (Ru3(O2CCH3)6.

[0063] The acidic medium may comprise H2SO4 or HClO,. The acidic medium may not be HC1. When the acidic medium is H2SO4, the solution may provide a different coordination environment for ruthenium 10ns. In HC1, Ru tends to form stable chloro-complcxcs, while in H2SO4, sulfate ligands coordinate differently, which may lead to distinct hydrolyzed or sulfate-bound species. This difference in precursor chemistry may affect the nucleation and growth of Ru during deposition and may advantageously enable the formation of submicron hep sheet structures at low loading, which may not be achieved under HO conditions. The depositing step b) may comprise applying an electrode potential of about 0.5 V to about -3 V against a counter electrode for a duration of about 0.01 minutes to about 200 minutes.

[0064] The deposited ruthenium may have a hexagonal closed packed (hep) structure.

[0065] The deposited ruthenium film may be present at a thickness in a range of from about 0.1 μm to about 1.0 μm, from about 0.1 μm to about 0.9 μm, from about 0.1 μm to about 0.8 μm, from about 0.1 μm to about 0.7 μm, from about 0.1 μm to about 0.6 μm. from about 0.1 μm to about 0.5 μm, from about 0.1 μm to about 0.4 μm, from about 0.1 μm to about 0.3 μm, from about 0.1 μm to about 0.2 μm, or from about 0.2 μm to about 1.0 μm, from about 0.3 μm to about 1.0 μm, from about 0.4 μm to about 1.0 μm, from about 0.5 μm to about 1.0 μm, from about 0.6 μm to about 1.0 μm, from about 0.7 μm to about 1.0 μm, from about 0.8 μm to about 1 .0 μm, from about 0.9 μm to about 1 .0 μm, or about 0.1 μm, about 0.2 μm, about 0.3 μm, about 0.4 μm, about 0.5 μm, about 0.6 μm, about 0.7 μm, about 0.8 μm, about 0.9 μm, about 1.0 μm, or any value or range therein. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that are within the stated range (s).

[0066] The deposited ruthenium may be present or comprised in the anode at an amount of from about 0.01 mg / cm-2to about 0.50 mg / cm-2, from about 0.01 mg / cm-2to about 0.45 mg / cm-2, from about 0.01 mg / cm2to about 0.40 mg / cm2. from about 0.01 mg / cm2to about 0.35 mg / cm2. from about 0.01 mg / cm2to about 0.30 mg / cm2. from about 0.01 mg / cm2to about 0.25 mg / cm2. from about 0.01 mg / cm2to about 0.20 mg / cm-2, from about 0.01 mg / cm-2to about 0.15 mg / cm-2, from about 0.01 mg / cm-2to about 0.10 mg / cm-2, from about 0.01 mg / cm-2to about 0.05 mg / cm-2, or from about 0.05 mg / cm-2to about 0.50 mg / cm-2, from about 0.10 mg / cm-2to about 0.50 mg / cm-2, from about 0.15 mg / cm-2to about 0.50 mg / cm-2, from about 0.20 mg / cm-2to about 0.50 mg / cm-2, from about 0.25 mg / cm-2to about 0.50 mg / cm-2, from about 0.30 mg / cm-2to about 0.50 mg / cm-2, from about 0.35 mg / cm-2to about 0.50 mg / cm-2, from about 0.40 mg / cm-2to about 0.50 mg / cm-2, from about 0.45 mg / cm-2to about 0.50 mg / cm-2, or about 0.01 mg / cm-2, about 0.05 mg / cm-2, about 0.10 mg / cm-2, about 0.15 mg / cm-2, about 0.20 mg / cm-2, about 0.25 mg / cm-2, about 0.30 mg / cm-2, about 0.35 mg / cm-2, about 0.40 mg / cm-2, about 0.45 mg / cm-2, about 0.50 mg / cm-2, or any value or range therein, based on the surface area of the substrate. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that are within the stated range(s).

[0067] The method may further comprise, before the depositing step b), the step al) pre-treating the substrate.

[0068] The pre-treating step al) may comprise soaking the substrate in an acid for a time period of about 1 minute to about 600 minutes.

[0069] The acid used in pre-treating step al) may be selected from the group consisting of nitric acid, sulfuric acid, hydrochloric acid, or combinations thereof.

[0070] The pre-treating step al) may be performed at a temperature of about 30 °C to about 70 °C. The pre-treating step al) may be performed for a time period of about 1 minute to about 600 minutes.

[0071] The pre-treating step al) may further comprise ultrasonication in ethanol and / or deionized water for 1 hour.

[0072] The method may not comprise a step of thermally annealing the deposited ruthenium after step b). The method may not comprise a step of chemically etching the deposited ruthenium after step b). Provided herein is an electrochemical cell comprising the anode produced by the method as disclosed herein.

[0073] Exemplary’, non-limiting embodiments of a use of an electrochemical cell will now be disclosed.

[0074] The use of the electrochemical cell as disclosed herein may be in water splitting, ammonia cracking, or as a fuel cell. Advantageously, the addition of sodium nitrate or any nitrate -containing wastewater may enable the ruthenium catalyst to reduce nitrate in the cathode, thereby producing ammonia and simultaneously purifying the nitrate from the wastewater.

[0075] Examples

[0076] Non-limiting examples of the invention and comparative examples will be further described in greater detail by’ reference to specific examples, which should not be construed as in any' way limiting the scope of the invention.

[0077] Example 1: Preparation of Ruthenium catalyst

[0078] Preparation of Ru precursor solution

[0079] Ruthenium chloride (RuCl3, analytical reagent, Sigma-Aldrich, Singapore) was dissolved in a 0.01 M to 6 M H2SO4 (Sigma- Aldrich, Singapore) to produce the Ru precursor solution at concentrations ranging from 0.001 mM to 10 M.

[0080] Preparation of carbon paper substrate

[0081] Carbon paper (fuel cell store) was soaked in a 1 : 1 - 1 : 10 nitric acid (Sigma- Aldrich, Singapore) : sulfuric acid (Sigma- Aldrich, Singapore) mixture for 2 hours.

[0082] Preparation ofTi substrate

[0083] A titanium substrate (fuel cell store) was ultrasonicated in ethanol for 1 hour, followed by deionized water for a further hour to remove surface oils. Subsequently, the substrate was soaked in 1-35% hydrochloric acid (Sigma- Aldrich, Singapore) at 30-70 °C for 1-600 minutes to remove the surface oxide layer.

[0084] Electrodeposition of Ru

[0085] Ru was deposited on a substrate under the following conditions: 0.5 - 3V against a reversible hydrogen electrode, for 0.01 mins to 200 mins.

[0086] Preparation of electrochemical cell

[0087] The electrochemical cell was assembled by placing the working, counter, and reference electrodes in the electrolyte solution, sealing the cell, and connecting to a potentiostat for electrodeposition.

[0088] Example 2: Characterization of catalyst

[0089] Digital photography was obtained by an iPhone 14 Pro camera to characterize the overall morphology of the anode. (Fig. 1 A)

[0090] Scanning Electron Microscopy (SEM) was performed on FESEM JEOL JSM-6340F to characterize the morphology of the catalyst (Figs. IB and 1C).

[0091] Transmission electron microscope was performed on TEM and JEOL 21 OOF. The sample was scraped from the surface of the electrode after the reaction for TEM characterization (Fig IE).

[0092] X-ray diffraction (XRD) was performed on Rigaku SmartLab 3kW XSPA to determine the crystal structure of the catalyst (Fig. ID).

[0093] The deposited ruthenium on the Ti substrate exhibited a film thickness of about 0.01 μm to about 1.0 μm, and was found to have a hexagonal closed packed (hcp) structure. The ruthenium also has a (0001) facet or a (10-10) facet.

[0094] In one example, the treated carbon-based support was immersed in an electrolyte containing 0.1 mM RuCI3and 0.5 M H2SO4. By applying a potential of -1.4 V vs. the reversible hy drogen electrode (RHE) for 60mins, nanosheets with a hexagonal close-packed (hep) crystal structure (Fig. ID) and a thickness of ~ 0.03 μm (Figs. IB, 1C) were deposited.

[0095] Example 3: Electrochemical performance of catalyst

[0096] All electrochemical measurements were conducted at room temperature in a standar d three - electrode cell with an O2-saturatcd 0.5 M H2SO4 electrolyte. The prepared electrodes were directly used for electrochemical testing, with a Pt mesh and a saturated Ag / AgCl electrode serving as the counter and reference electrodes, respectively. LSV tests were recorded at a scan rate of 5 mV s-1 to evaluate the activity (Fig. 3A). The chronopotentiometry' (CP) method was used to evaluate the stability' of the catalyst (Fig. 2). All potentials measured against Ag / AgCl were converted to the reversible hydrogen electrode (RHE) scale using: E (potential, versus RHE) = E(vcrsus Ag / AgCl) + 0.198 V + 0.0591 x pH. E (overpotential) = E(potential at 10 mA cm'2) - 1.23 V.

[0097] Average degradation rate = E (degradation) / time

[0098] The 3-electrode system, consisting of a working electrode, counter electrode, and reference electrode, is a well-known method for evaluating half-reactions. Given that overall water splitting consists of two half-reactions — hydrogen evolution reaction (HER) at the cathode and oxygen evolution reaction (OER) at the anode — a 3-electrode system was used here to assess the ruthenium- based anode.

[0099] Composed of nano -cry stallites, the sub-micron Ru sheets (Figs. IB and 1C) provide a larger active area than bulk Ru, while the in-situ formation of a surface oxide film (Fig. IE) during OER significantly inhibits dissolution, thereby drastically improving the OER stability of metallic Ru in acidic environments.

[0100] Comparative Examples

[0101] Comparative Example 1: Ru-based electrocatalysts

[0102] The OER performance of the cataly st as synthesized above was compared to conventional Ru-based catalysts, demonstrating comparable OER performance, and much higher stability while having lower catalyst loading than Table 1: Summary of acidic OER Performance of comparative embodiments of Ru-based electrocatalysts

[0103] As can be seen from Table 1, the ruthenium catalyst of the present application had the lowest loading when compared to conventional ruthenium-based electrocatalysts and with comparable activity, much higher lifetime and exhibiting almost no degradation. It can thus be concluded that the ruthenium catalyst of the present application is superior to other ruthenium-based electrocatalysts.

[0104] Industrial Applicability

[0105] The present invention relates to electrochemical cells comprising ruthenium electrodes such as anodes. The electrochemical cells of the present invention may be used in applications such as water splitting, ammonia cracking, or as a fuel cell.

[0106] It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.

Claims

Claims1. An electrochemical cell comprising: an anode comprising a catalyst consisting essentially of ruthenium disposed on a substrate, wherein the ruthenium is present as a film with a thickness of about 0. 1 μm to about 1 .0 μm; a cathode; and an exchange membrane separating the anode and the cathode.

2. The electrochemical cell of claim 1, wherein the amount of the ruthenium is about 0.01 mg / cm2to about 0.5 mg / cm2based on the surface area of the substrate.

3. The electrochemical cell of claim 1 or 2, wherein the ruthenium has a hexagonal close - packed (hep) structure.

4. The electrochemical cell of any one of claims 1 to 3, wherein the substrate is selected from the group consisting of titanium (Ti), carbon (C), fluorine -doped tin oxide (FTO), and glassy carbon.

5. The electrochemical cell of any one of claims 1 to 4, wherein the cathode comprises the same catalyst as the anode.

6. A method of preparing an electrode comprising a catalyst consisting essentially of ruthenium, the method comprising the steps of: a) providing a solution of a ruthenium precursor at a concentration of about 1 pM to about 10 M in an acidic medium; and b) electrochemically depositing the ruthenium onto a substrate to achieve a ruthenium film with a thickness of about 0.1 μm to about 1.0 μm, thereby forming the electrode.

7. The method of claim 6, wherein the precursor is selected from the group consisting of RuCI and ruthenium acetate (Ru3(O2CCH3)68. The method of claim 6 or 7, wherein the acidic medium comprises H2SO4 or HCIO4.

9. The method of any one of claims 6 to 8, wherein the depositing step b) comprises applying an electrode potential of about 0.5 V to about -3 V against a reference electrode for a duration of about 0.01 minutes to about 200 minutes.

10. The method of any one of claims 6 to 9, wherein the ruthenium is loaded at a loading of about 0.01 mg / cm2to about 0.5 mg / cm2based on the surface area of the substrate.

11. The method of any one of claims 6 to 10, wherein the substrate is selected from the group consisting of titanium (Ti), carbon (C), fluorine -doped tin oxide (FTO), and glassy carbon.

12. The method of any one of claims 6 to 11, further comprising, before the depositing step b), the step al ) pre-treating the substrate.

13. The method of claim 12, wherein the pre-treating step al) comprises soaking the substrate in an acid for a time period of about 1 minute to about 600 minutes.

14. An electrochemical cell comprising the electrode produced by the method of any one of claims 6 to 13.

15. Use of an electrochemical cell of any one of claims 1 to 5, or 14, in water splitting, ammonia cracking, or as a fuel cell .

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